1. The Field of the Invention
The present invention generally relates to medical devices. More particularly, the present invention relates to mechanisms for selectively restraining medical devices and methods of manufacturing such mechanisms.
2. The Relevant Technology
Human blood vessels often become occluded or blocked by plaque, thrombi, other deposits, or material that reduce the blood carrying capacity of the vessel. Should the blockage occur at a critical place in the circulatory system, serious and permanent injury, and even death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected.
Several procedures are now used to open these stenosed or occluded blood vessels in a patient caused by the deposit of plaque or other material on the walls of the blood vessels. These procedures can include angioplasty, atherectomy, and stenting. Unfortunately, such percutaneous interventional procedures, i.e., angioplasty, atherectomy, and stenting, often dislodge material from the vessel walls. This dislodged material can enter the bloodstream, and may be large enough to occlude smaller downstream vessels, potentially blocking blood flow to tissue. The resulting ischemia poses a serious threat to the health or life of a patient if the blockage occurs in critical tissue, such as the heart, lungs, kidneys, or brain, resulting in a stroke or infarction.
Some existing devices and technology use a medical device, such as an embolic protection device to limit or prevent the flow of dislodged material downstream from the occluded or blocked portion of the vessel. The existing technology includes balloon-type devices and filter-type devices. Balloon-type embolic protection devices include one or more balloons that can be inflated at a location distal to the occluded or blocked portion of the vessel. This type of device is useful in preventing the flow of dislodged material, but also prevents blood from flowing downstream. These balloon-type devices can only be used for a limited period of time; else the lack of blood flow to particular areas of the body may result in undesirable side effects, such as stroke, seizures, or the like.
In contrast, filter-type embolic protection devices usually include a filter that expands under the influence of one or more biased struts. The filter is formed from an organic or inorganic polymer film which includes pores or openings that allow the blood to pass while at the same time preventing larger debris from passing downstream. The filter-type device allows blood to flow downstream of the occluded or blocked portion of the vessel, which is an advance over the balloon-type devices. Unfortunately, there are significant problems associated with positioning the filter-type device prior to deployment to filter dislodged material.
The filter and struts of the filter-type device are usually compressed or restrained in some manner in order to be easily deployed within the vasculature of the patient. Usually, a catheter compresses or restrains the filter-type device. Locating the catheter at the occluded or blocked portion of the vessel occurs as a physician or clinician advances the catheter containing the filter along a guide wire positioned within the lumen of the patient. Positioning the catheter at a location for deploying the filter-type device requires passing the catheter through the occluded or blocked region of the vessel. Since the outside diameter of the catheter is far greater than the guide wire, moving the catheter past the occluded or blocked region of the vessel can dislodge embolic material. As mentioned above, this dislodged material can occlude smaller downstream vessels, potentially blocking blood flow to tissue and resulting in a stroke or infarction. Additionally, moving the catheter through the tortuous anatomy of the patient can damage portions of vessels and other body lumens; resulting in an increased probability of adverse procedural outcomes.
It is desirable to have a mechanism for restraining the filter and struts of a filter-type device which results in a smaller outside diameter than a catheter. By reducing the profile of the deployment mechanism, the possibility of dislodging materials during insertion of the filter-type device is reduced. In addition, because of the small and delicate nature of the filter assembly, it is desirable that the restraining mechanism be easily manufactured with as few and as simple of steps as possible.